大洋转换断层演化过程中下地壳变质条件的增加

IF 3.2 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
Peter Haas, Myron F. H. Thomas, Christian Heine, Jörg Ebbing, Andrey Seregin, Jimmy van Itterbeeck
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引用次数: 0

摘要

摘要海洋转换断层连接着相互滑动的活动扩张脊段。按照传统观点,转换断层被认为是保守的,不会增加或破坏物质。然而,最近的研究表明,转换断层区域的地壳在不同时期会发生变形。我们将高分辨率三维宽带地震数据与船载电位场数据相结合,研究了圣多美和普林西比近海几内亚湾东部阿尔卑斯-安普顿时代大洋地壳中的古断层带。该地区地壳的特点是上层地壳薄、反射率高,下层地壳厚,几乎是地震透明层,由局部倾斜反射体组成,以前被解释为挤出熔岩流。这一层界定了潜在野外数据反演和前向建模的目标区域。选取的地震层被用作地壳模型的几何边界。首先,我们对下部地壳进行横向参数反演,提供密度和磁感应强度的垂直列。其次,我们使用聚类方法对估计值进行分类,并识别出具有共同参数关系的五个组。第三,与第一步的简单反演相比,我们使用聚类的下地壳域定义研究区域的一致三维模型,该模型与地震结构和地质概念相一致。最终模型显示,埋藏断裂带附近存在异常的低感度和中高密度,这反映了压力和温度条件的增加以及变质面的变化。我们的模型表明,在大洋地壳形成过程中,构造活动增强,其中延伸部分在转换区达到顶峰。这些结果与最近的研究相一致,并加强了海脊-转换交汇处非保守特征的印象。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Increased metamorphic conditions in the lower crust during oceanic transform fault evolution
Abstract. Oceanic transform faults connect the segments of active spreading ridges that slide past each other. In a classical view, transform faults are considered as conservative, where no material is added or destroyed. Recent studies, however, suggest that the crust in the transform fault region is deformed during different episodes. We combine high resolution 3D broadband seismic data with shipborne potential field data to study ancient fault zones in Albian-Aptian aged oceanic crust in the eastern Gulf of Guinea offshore São Tomé and Príncipe. The crust in this region is characterized by a thin, high-reflective upper crust, which is underlain by a thick, almost seismically transparent unit that comprises localized dipping reflectors, previously interpreted as extrusive lava flows. This layer defines the target area for inversion and forward modelling of the potential field data. The picked seismic horizons are used as geometrical boundaries of the crustal model. First, we perform a lateral parameter inversion for the lower crust, which provides vertical columns of density and magnetic susceptibility. Second, we sort the estimated values using a clustering approach and identify five groups with common parameter relationships. Third, we use the clustered lower crustal domains to define a consistent 3D model of the study area that aligns with the seismic structure and geological concepts, preferred to the simple inversion of the first step. The final model shows anomalous low susceptibility and medium to high density close to the buried fracture zones, which reflects increasing pressure and temperature conditions accompanied by a change of metamorphic facies. Our model indicates enhanced tectonic activity with an extensional component during the formation of oceanic crust that culminates in the transform region. These results are in line with recent studies and strengthen the impressions of a non-conservative character of ridge-transform intersections.
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来源期刊
Solid Earth
Solid Earth GEOCHEMISTRY & GEOPHYSICS-
CiteScore
6.90
自引率
8.80%
发文量
78
审稿时长
4.5 months
期刊介绍: Solid Earth (SE) is a not-for-profit journal that publishes multidisciplinary research on the composition, structure, dynamics of the Earth from the surface to the deep interior at all spatial and temporal scales. The journal invites contributions encompassing observational, experimental, and theoretical investigations in the form of short communications, research articles, method articles, review articles, and discussion and commentaries on all aspects of the solid Earth (for details see manuscript types). Being interdisciplinary in scope, SE covers the following disciplines: geochemistry, mineralogy, petrology, volcanology; geodesy and gravity; geodynamics: numerical and analogue modeling of geoprocesses; geoelectrics and electromagnetics; geomagnetism; geomorphology, morphotectonics, and paleoseismology; rock physics; seismics and seismology; critical zone science (Earth''s permeable near-surface layer); stratigraphy, sedimentology, and palaeontology; rock deformation, structural geology, and tectonics.
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